Burning crop residue exposes farmers to cancer-causing chemicals: Study

Burning crop residue exposes farmers to smoke containing cancer-causing chemicals which farmers and villagers ignorantly inhale as these chemicals stay in the air for a few days.

The practice, common in Indian farmlands, may pose a new health threat, say a group of Indian scientists who want the Central government to monitor the level of these chemicals in the air in post-harvest seasons in order to understand how serious and wide-ranging the perceived health threat is.

Three researchers from the Indian Institute of Science, Education and Research (IISER), Mohali, measured the level of these chemicals–known as benzenoids–in the air near Chandigarh in October and November, 2012, to compare the level of these chemicals before and after paddy crop residue was burnt.

Compared to October, there is 300 per cent increase in benzenoid level in November when dried stumps of paddy crops are put to flame. Similar “massive” presence of these chemicals are expected when wheat crop residues are burnt.

“Such high levels of benzenoids for 1-2 months in a year aggravates smog and can enhance cancer risks in northwestern India,” the researchers reported in the June 25 issue of Current Science.

“As a public health threat it is serious. The highest cancer risk from the carcinogenic chemicals released by paddy residue burning would be in the rural and agricultural areas where the burning actually takes place for 4-6 weeks in a year, as the exposure level would be highest there,” team leader Vinayak Sinha told Deccan Herald.

While busy traffic intersection in large cities like Delhi will have a high level of these chemicals, paddy residue burning may be a key contributor to high benzenoid levels in the countryside.

Prevailing weather conditions like wind flow will determine how long these chemicals will remain in the air and in what concentration. Dilution will reduce their harmful effects even though two chemicals–benzene (4.7 days) and toluene (1.6 days)–have a long life. Independent scientists, however, feel the linkage between higher levels of chemicals in the air and cancer risk is somewhat premature and more intense research is required.

“The data generated so far have been limited to two events. More data needed to define this correlation as a causality. The correlation between biomass burning and the health risk, such as increased incidence of cancer, is somewhat premature and requires more scientific validation,” commented S Sivaram, former director of National Chemical Laboratory, Pune, who was not associated with the study.

The IISER team cites the example of paddy growing Malwa region, which has high cancer prevalence. But they admit they are far from establishing a cause-and-effect relations in Malwa and more data was required.

“Exposure of the population to sustained high levels of carcinogenic benzenoids in the air they breathe for several months in a year could certainly be a contributory factor for cancer prevalence and warrants detailed multidisciplinary epidemiological and environmental studies,” the scientists said.